According to the defect of the high peak-to-average-power ratio (PAPR) in optical orthogonal frequency division multiplexing (OFDM) systems, the PAPR reduction technology based on the partial transmission sequences (PTS) method has been deeply studied. An improved enhanced-iterative-algorithm-PTS (EIA-PTS) technology is proposed. The proposed EIA-PTS technology, compared with the original PTS (O-PTS), can reduce the computational complexity. The simulation analysis shows that the computational complexity of the O-PTS method grows exponentially with an increase in the number of both subblocks and phase factors, while the computational complexity of the EIA-PTS technology basically remains stable and is lower than that of the O-PTS method. On the basis of the proposed EIA-PTS technology, an improved EIA-PTS-Clipping combined PAPR reduction technology that combines EIA-PTS technology with clipping technology is proposed. The simulation result shows the proposed EIA-PTS-Clipping combined PAPR reduction technology, compared with the previous proposed EIA-PTS technology, can further improve the PAPR reduction performance and has a higher application value because it can have a better tradeoff between the bit error rate performance and PAPR reduction effect for optical OFDM systems.
An adaptive algorithm of fine synchronization for coherent optical orthogonal frequency division multiplexing
(CO-OFDM) transmission system is proposed. The whole synchronization is separated into two steps. In the first step,
we use an auto-correlation-style algorithm to achieve the coarse symbol synchronization. In the second step, the
proposed algorithm is used to achieve the fine synchronization. The merit of the proposed algorithm is that it can realize
fine synchronization under different environments without adjusting the detect-threshold of timing metric in a
dynamically reconfiguration network. The numerical experiment result demonstrates that the proposed algorithm
achieves fine synchronization under different signal noise ratio (SNR) conditions after 6 fiber-spans transmission.
In this paper, the three ameliorated new coding schemes of the Super-FEC (Forward Error Correction) concatenatedcodes
(namely, the inner-outer concatenated-code, the parallel concatenated-code and the successive concatenated-code
with interleaving) are proposed after the development trend of high-rate optical transmission systems and the defects of
the FEC codes in the current optical transmission systems have been analyzed. The system simulation of the inner-outer
concatenated-codes is implemented and the schemes of encoding/decoding the parallel concatenated-codes are proposed.
Furthermore, the two successive concatenated-codes with interleaving of the RS(255,239)+RS(255,239) code and the
RS(255,239)+RS(255,223) code are simulated, and the analyses for the simulation results show that the two successive
concatenated-codes with interleaving, compared with the classic RS (255,239) code and other codes, are a superior code
type with the advantages of the better correction error, moderate redundancy and easy realization. And their net coding
gains (NCG) are respectively 1.5dB, 2.5dB more than that of the classic RS(255,239) code at the BER (Bit Error Rate) of
10-12. At last, based on the ITU-T G.709, the frame format of the new concatenated-code on applying in high-rate optical
transmission systems is proposed and designed, this lays a firm foundation in order to design its hardware in future and
pioneers a direction in its physical application.